A novel LC VCO topology with switched current source is presented. Theoretical analysis is given to show the reduction of cross-paired transistors?? drain current duty cycle with the implementation of current source switching, which reduces the upconversion of 1/f noise and also provides noise shaping by directly reducing 1/f noise. A 5.25-5.5 GHz LC VCO has been fabricated and measured for the proposed topology, achieving a FOM of 2191 dBc/Hz, which is among the best published FOM results for 5??6 GHz VCOs in standard CMOS process.